Various user input devices can provide an interactive surface configured to receive user inputs. For example, a touch screen or touch-sensitive pad can be used as input devices to different computing devices, including tablet computing devices, mobile phones, and laptop computing devices. As a further example, capacitive touch screens can detect an input when a human body (or a conductive object contacting the human body) touches the screen, but not when a non-conductive object touches the screen. This distinction is generally due to the electrical characteristics of the human body that can change the capacitance of the screen.